This invention relates to a logarithmic potentiometer circuit comprising an adjustable ohmic resistance element.
Logarithmic potentiometers are well known and are described, for example, in "Baiers Electronik Lexikon", Francksche Verlagsbuchhandlung, Stuttgart, 1974, p. 406. If a connection terminal and the tapping on a logarithmic potentiometer are electrically interconnected, an adjustable ohmic resistance element is obtained having an exponential resistance characteristic, which can be represented as a straight line when the ohmic resistance is plotted logarithmically on the ordinate of the characteristic diagram. Such potentiometers can be constructed as film potentiometers or as wire potentiometers. The manufacture of logarithmic wire potentiometers having an exponential characteristic that can be accurately determined is comparatively expensive, however, because in this case high-resistance wire is wound onto a starting body that is insulating and is manufactured precisely. Also, film potentiometers whose actual characteristic fully corresponds to a determined characteristic can be manufactured only with great technical efforts.
An object of the present invention is to provide an inexpensive potentiometer circuit having an approximately logarithmic characteristic that can be accurately determined.